116 THE DEVELOPMENT 



men, to the exclusion of every other structure. It must be 

 remembered that this is more apparent than real, and only applies 

 to the particular section drawn, as, of course, the bladder finds a 

 place somewhere within the cavity, although not shown in this 

 diagram. 'I'he tail also stretches far beyond the limits of the 

 l)late. This spirally-coiled intestine is of the most simple 

 structure, consisting, for the most part, of a single row of rounded 

 cells, some of which, however, have in places begun to flatten and 

 form rough parallelograms, whilst others are distinctly pointed 

 instead of rounded on the outside. 



Unless these minute difterences in form are indications 

 thereof, there are no signs of the villi which at a later stage line 

 portions of this tube, and especially in the adult state, when the 

 tadpole has become a frog, and the fish has been converted into 

 the amphibian. No wonder that the horny cases of the Glochidia^ 

 mentioned in a previous article, disagreed with the delicate 

 digestive powers of these little creatures ! ! 



At the same time that these changes were progressing in the 

 abdominal regions, others not less great and interesting were 

 taking place in the region of the gills and lungs. The right gill 

 atrophies before the left, both ultimately becoming covered by the 

 opercular membrane ; but for some days after the right gill has 

 been quite enclosed, water finds its way into the left side through 

 a small opening to bathe the internal branchiae, which now exclu- 

 sively carry on the work of respiration. 



These internal branchiae are situated in branchial chambers, 

 whose walls are largely composed of cartilage, to which the 

 branchiae are attached. The branchiae are in rows, the outermost 

 ones terminating in long tufts. The median tufts are not so long, 

 but each ridge is furnished with a blood-vessel running around its 

 inside edge, and by means of which the blood it contains is 

 exposed to a large surface of fresh oxygenated water for aeration. 

 Whitney, in the " Royal Microscopical Society's Transactions, 

 1867," p. 43, gives a lucid account of his experiments on the 

 living tadpole, by which he was able to demonstrate the connec- 

 tion between these and the true lungs. He there states that 

 three arterial trunks arise from the heart, and convey the blood to 

 the outer gills whilst the inner are forming, but at the same time 



